Re: Virtqemud wants to unlink /dev/urandom

Martin Kletzander <mkletzan@xxxxxxxxxx> · Mon, 14 Mar 2022 12:45:39 +0100

[adding back libvir-list to the Cc]

On Fri, Mar 11, 2022 at 03:55:03PM +0100, Nikola Knazekova wrote:
Hey Martin,

thanks for your resposne.

I don't know if it is happening in the mount namespace. Can you look at the
logs in attachment?

It was happening on clear install on F35, F36 and on older versions
probably too.
But it is only an issue in the new selinux policy for libvirt. In old
selinux policy is allowed for virtd to unlink /dev/urandom char files.
I just wanted to be sure if it is ok to allow it for virtqemud.

That actually might be the case, that it actually does set the context
on /dev/urandom correctly and then the unlink fails for virtqemud since
the selinux policy only accounts for libvirtd even though we switched to
modular daemons making virtqemud the one to do the work.

@Michal can you confirm what I'm guessing here since you did a lot of
the mount namespace work which I presume is what contributes to the
issue here.

In the meantime, would you mind trying this with the mount namespace
feature turned off in /etc/libvirt/qemu.conf like this:

namespaces = []

Thanks.

Regards,
Nikola

On Thu, Feb 24, 2022 at 3:00 PM Martin Kletzander <mkletzan@xxxxxxxxxx>
wrote:

On Thu, Feb 24, 2022 at 01:41:50PM +0100, Nikola Knazekova wrote:
>Hi,
>
>when I am creating virtual machine on system with new SELinux policy for
>Libvirt, I am getting this error message:
>
>Unable to complete install: 'Unable to create device /dev/urandom: File
>exists'
>Traceback (most recent call last):
>  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 65, in
>cb_wrapper
>    callback(asyncjob, *args, **kwargs)
>  File "/usr/share/virt-manager/virtManager/createvm.py", line 2001, in
>_do_async_install
>    installer.start_install(guest, meter=meter)
>  File "/usr/share/virt-manager/virtinst/install/installer.py", line 701,
>in start_install
>    domain = self._create_guest(
>  File "/usr/share/virt-manager/virtinst/install/installer.py", line 649,
>in _create_guest
>    domain = self.conn.createXML(install_xml or final_xml, 0)
>  File "/usr/lib64/python3.10/site-packages/libvirt.py", line 4393, in
>createXML
>    raise libvirtError('virDomainCreateXML() failed')
>libvirt.libvirtError: Unable to create device /dev/urandom: File exists
>
>And SELinux denial, where SELinux prevents virtqemud to unlink character
>device /dev/urandom:
>
>time->Wed Feb 23 19:30:33 2022
>type=PROCTITLE msg=audit(1645662633.819:930):

>proctitle=2F7573722F7362696E2F7669727471656D7564002D2D74696D656F757400313230
>type=PATH msg=audit(1645662633.819:930): item=1 name="/dev/urandom"
inode=6
>dev=00:44 mode=020666 ouid=0 ogid=0 rdev=01:09
>obj=system_u:object_r:urandom_device_t:s0 nametype=DELETE cap_fp=0
cap_fi=0
>cap_fe=0 cap_fver=0 cap_frootid=0
>type=PATH msg=audit(1645662633.819:930): item=0 name="/dev/" inode=1
>dev=00:44 mode=040755 ouid=0 ogid=0 rdev=00:00
>obj=system_u:object_r:tmpfs_t:s0 nametype=PARENT cap_fp=0 cap_fi=0
cap_fe=0
>cap_fver=0 cap_frootid=0
>type=CWD msg=audit(1645662633.819:930): cwd="/"
>type=SYSCALL msg=audit(1645662633.819:930): arch=c000003e syscall=87
>success=no exit=-13 a0=7f9418064f50 a1=7f943909c930 a2=7f941d0ef6d4 a3=0
>items=2 ppid=6722 pid=7196 auid=4294967295 uid=0 gid=0 euid=0 suid=0
>fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="rpc-worker"
>exe="/usr/sbin/virtqemud" subj=system_u:system_r:virtqemud_t:s0 key=(null)
>type=AVC msg=audit(1645662633.819:930): avc:  denied  { unlink } for
> pid=7196 comm="rpc-worker" name="urandom" dev="tmpfs" ino=6
>scontext=system_u:system_r:virtqemud_t:s0
>tcontext=system_u:object_r:urandom_device_t:s0 tclass=chr_file
permissive=0
>
>Is this expected behavior?
>

The error is not, but creating and removing /dev/urandom is fine, as far
as it happens in the mount namespace of the domain, which we create and
as such we also need to create some basic /dev structure in there.

Unfortunately this error does not show whether it is happening in the
mount namespace, although it should definitely _not_ happen outside of it.

Does this happen on clean install?  What is the version of libvirt and
the selinux policy?  What's the distro+version of the system?  Would you
mind capturing the debug logs and attaching them?

How to capture debug logs: https://libvirt.org/kbase/debuglogs.html

>Thanks,
>Nikola

2022-03-04 03:08:28.053+0000: starting up libvirt version: 8.0.0, package: 2.fc36 (Fedora Project, 2022-01-20-17:44:09, ), qemu version: 6.2.0qemu-6.2.0-5.fc36, kernel: 5.17.0-0.rc5.102.fc36.x86_64, hostname: fedora
LC_ALL=C \
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin \
HOME=/var/lib/libvirt/qemu/domain-4-fedora35-3 \
XDG_DATA_HOME=/var/lib/libvirt/qemu/domain-4-fedora35-3/.local/share \
XDG_CACHE_HOME=/var/lib/libvirt/qemu/domain-4-fedora35-3/.cache \
XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain-4-fedora35-3/.config \
/usr/bin/qemu-system-x86_64 \
-name guest=fedora35-3,debug-threads=on \
-S \
-object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/var/lib/libvirt/qemu/domain-4-fedora35-3/master-key.aes"}' \
-machine pc-q35-6.2,usb=off,vmport=off,dump-guest-core=off,memory-backend=pc.ram \
-accel kvm \
-cpu host,migratable=on \
-m 2048 \
-object '{"qom-type":"memory-backend-ram","id":"pc.ram","size":2147483648}' \
-overcommit mem-lock=off \
-smp 2,sockets=2,cores=1,threads=1 \
-uuid 818068b5-c72b-475c-a960-231f29f60464 \
-no-user-config \
-nodefaults \
-chardev socket,id=charmonitor,fd=28,server=on,wait=off \
-mon chardev=charmonitor,id=monitor,mode=control \
-rtc base=utc,driftfix=slew \
-global kvm-pit.lost_tick_policy=delay \
-no-hpet \
-no-shutdown \
-global ICH9-LPC.disable_s3=1 \
-global ICH9-LPC.disable_s4=1 \
-boot strict=on \
-device pcie-root-port,port=16,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 \
-device pcie-root-port,port=17,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 \
-device pcie-root-port,port=18,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 \
-device pcie-root-port,port=19,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 \
-device pcie-root-port,port=20,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 \
-device pcie-root-port,port=21,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 \
-device pcie-root-port,port=22,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 \
-device pcie-root-port,port=23,chassis=8,id=pci.8,bus=pcie.0,addr=0x2.0x7 \
-device pcie-root-port,port=24,chassis=9,id=pci.9,bus=pcie.0,multifunction=on,addr=0x3 \
-device pcie-root-port,port=25,chassis=10,id=pci.10,bus=pcie.0,addr=0x3.0x1 \
-device pcie-root-port,port=26,chassis=11,id=pci.11,bus=pcie.0,addr=0x3.0x2 \
-device pcie-root-port,port=27,chassis=12,id=pci.12,bus=pcie.0,addr=0x3.0x3 \
-device pcie-root-port,port=28,chassis=13,id=pci.13,bus=pcie.0,addr=0x3.0x4 \
-device pcie-root-port,port=29,chassis=14,id=pci.14,bus=pcie.0,addr=0x3.0x5 \
-device qemu-xhci,p2=15,p3=15,id=usb,bus=pci.2,addr=0x0 \
-device virtio-serial-pci,id=virtio-serial0,bus=pci.3,addr=0x0 \
-blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/fedora35-3.qcow2","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}' \
-blockdev '{"node-name":"libvirt-2-format","read-only":false,"discard":"unmap","driver":"qcow2","file":"libvirt-2-storage","backing":null}' \
-device virtio-blk-pci,bus=pci.4,addr=0x0,drive=libvirt-2-format,id=virtio-disk0,bootindex=2 \
-blockdev '{"driver":"file","filename":"/home/n/Downloads/Fedora-Workstation-Live-x86_64-35-1.2.iso","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
-blockdev '{"node-name":"libvirt-1-format","read-only":true,"driver":"raw","file":"libvirt-1-storage"}' \
-device ide-cd,bus=ide.0,drive=libvirt-1-format,id=sata0-0-0,bootindex=1 \
-netdev tap,fd=29,id=hostnet0,vhost=on,vhostfd=31 \
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:81:d4:90,bus=pci.1,addr=0x0 \
-chardev pty,id=charserial0 \
-device isa-serial,chardev=charserial0,id=serial0 \
-chardev socket,id=charchannel0,fd=27,server=on,wait=off \
-device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0 \
-chardev spicevmc,id=charchannel1,name=vdagent \
-device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0 \
-device usb-tablet,id=input0,bus=usb.0,port=1 \
-audiodev '{"id":"audio1","driver":"spice"}' \
-spice port=5900,addr=127.0.0.1,disable-ticketing=on,image-compression=off,seamless-migration=on \
-device virtio-vga,id=video0,max_outputs=1,bus=pcie.0,addr=0x1 \
-device ich9-intel-hda,id=sound0,bus=pcie.0,addr=0x1b \
-device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0,audiodev=audio1 \
-chardev spicevmc,id=charredir0,name=usbredir \
-device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 \
-chardev spicevmc,id=charredir1,name=usbredir \
-device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 \
-device virtio-balloon-pci,id=balloon0,bus=pci.5,addr=0x0 \
-object '{"qom-type":"rng-random","id":"objrng0","filename":"/dev/urandom"}' \
-device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.6,addr=0x0 \
-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
-msg timestamp=on
char device redirected to /dev/pts/2 (label charserial0)
2022-03-04T03:09:24.261105Z qemu-system-x86_64: terminating on signal 15 from pid 8179 (/usr/sbin/virtqemud)
2022-03-04 03:09:24.461+0000: shutting down, reason=destroyed

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